Reconstrainable stent delivery system

ABSTRACT

The stent of the present invention combines a helical strut band interconnected by coil elements. This structure provides a combination of attributes that are desirable in a stent, such as, for example, substantial flexibility, stability in supporting a vessel lumen, cell size and radial strength. The structure of the stent of the present invention provides a predetermined geometric relationship between the helical strut band and interconnected coil.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/103,073, filed Oct. 6, 2008, the entirety of which ishereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to a self expanding stent and delivery systemfor a self expanding stent. The delivery system allows forreconstraining the stent into the delivery catheter simultaneouslyallowing the stent to change lengths and rotate inside the deliverycatheter if required. This invention also pertains to a delivery systemfor self expanding stent that foreshortens an appreciable amount, forexample more than about 10%.

2. Description of the Related Art

Most commercial self expanding stents are not designed to be recaptured(reconstrained) into the delivery system once the stent has started toexpand into the target vessel, artery, duct or body lumen. It would beadvantageous for a stent to be able to be recaptured after the stent hasstarted to deploy in the event that the stent is placed in an incorrector suboptimal location, the stent could be recaptured and redeployed orrecaptured and withdrawn. A recapturable stent and delivery system wouldconstitute a major safety advantage over non-recapturable stent anddelivery systems.

Many conventional self expanding stents are designed to limit the stentforeshortening to an amount that is not appreciable. Stentforeshortening is a measure of change in length of the stent from thecrimped or radial compressed state as when the stent is loaded on or ina delivery catheter to the expanded state. Percent foreshortening istypically defined as the change in stent length between the deliverycatheter loaded condition (crimped) and the deployed diameter up to themaximum labeled diameter divided by the length of the stent in thedelivery catheter loaded condition (crimped). Stents that foreshorten anappreciable amount are subject to more difficulties when being deployedin a body lumen or cavity, such as a vessel, artery, vein, or duct. Thedistal end of the stent has a tendency to move in a proximal directionas the stent is being deployed in the body lumen or cavity.Foreshortening may lead to a stent being placed in an incorrect orsuboptimal location. Delivery systems that can compensate for stentforeshortening would have many advantages over delivery systems that donot.

A stent is a tubular structure that, in a radially compressed or crimpedstate, can be inserted into a confined space in a living body, such as aduct, an artery or other vessel. After insertion, the stent can beexpanded radially at the target location. Stents are typicallycharacterized as balloon-expanding (BX) or self-expanding (SX). Aballoon-expanding stent requires a balloon, which is usually part of adelivery system, to expand the stent from within and to dilate thevessel. A self expanding stent is designed, through choice of material,geometry, or manufacturing techniques, to expand from the crimped stateto an expanded state once it is released into the intended vessel. Incertain situations higher forces than the expanding force of the selfexpanding stent are required to dilate a diseased vessel. In this case,a balloon or similar device might be employed to aid the expansion of aself expanding stent.

Stents are typically used in the treatment of vascular and non-vasculardiseases. For instance, a crimped stent may be inserted into a cloggedartery and then expanded to restore blood flow in the artery. Prior torelease, the stent would typically be retained in its crimped statewithin a catheter and the like. Upon completion of the procedure, thestent is left inside the patient's artery in its expanded state. Thehealth, and sometimes the life, of the patient depends upon the stent'sability to remain in its expanded state.

Many conventional stents are flexible in their crimped state in order tofacilitate the delivery of the stent, for example, within an artery. Feware flexible after being deployed and expanded. Yet, after deployment,in certain applications, a stent may be subjected to substantial flexingor bending, axial compressions and repeated displacements at pointsalong its length, for example, when stenting the superficial femoralartery. This can produce severe strain and fatigue, resulting in failureof the stent.

A similar problem exists with respect to stent-like structures. Anexample would be a stent-like structure used with other components in acatheter-based valve delivery system. Such a stent-like structure holdsa valve which is placed in a vessel.

SUMMARY OF THE INVENTION

The present invention comprises a catheter delivery system forself-expanding stents. The reconstrainable stent delivery system of thepresent invention comprises a proximal end and distal end, which includeinner and outer members, typically shafts or catheter or outer sheath ofthe catheter, which is crimped onto a slider at the proximal end of thestent. The slider can rotate about and move longitudinally along one ofan inner shaft or tube, such as the guide wire tube, such that theproximal end of the stent can move distally as the stent deploys. Apusher can be used on the guide wire tube such that the guide wire tube,pusher, and stent move proximally relative to the outer sheath andreconstrain the stent in the outer sheath. Furthermore, the pusher andguide wire tube could move distally as the outer sheath retractsproximally for stent deployment to accommodate foreshortening.

The delivery system can also include a spring element in the catheterdelivery system that will react the axial load at the proximal end ofthe stent during stent deployment. A spring element as described canbias the axial movement of the stent inside the delivery catheter tomove distally as the stent is deployed. This biased movement isbeneficial for stents that foreshorten an appreciable amount as thebiased movement reduce the amount of movement at the distal end of thestent during stent deployment.

The catheter delivery system can be used to deploy stents in iliac,femoral, popliteal, carotid, neurovascular or coronary arteries,treating a variety of vascular disease states.

The stent of the present invention combines a helical strut member orband interconnected by coil elements. This structure provides acombination of attributes that are desirable in a stent, such as, forexample, substantial flexibility, stability in supporting a vessellumen, cell size and radial strength. However, the addition of the coilelements interconnecting the helical strut band complicates changing thediameter state of the stent. Typically, a stent structure must be ableto change the size of the diameter of the stent. For instance, a stentis usually delivered to a target lesion site in an artery while in asmall diameter size state, then expanded to a larger diameter size statewhile inside the artery at the target lesion site. The structure of thestent of the present invention provides a predetermined geometricrelationship between the helical strut band and interconnected coilelements in order to maintain connectivity at any diameter size state ofthe stent.

The stent of the present invention is a self-expanding stent made fromsuperelastic nitinol. Stents of this type are manufactured to have aspecific structure in the fully expanded or unconstrained state.Additionally, a stent of this type must be able to be radiallycompressed to a smaller diameter, which is sometimes referred to as thecrimped diameter. Radially compressing a stent to a smaller diameter issometimes referred to as crimping the stent. The difference in diameterof a self-expanding stent between the fully expanded or unconstraineddiameter and the crimped diameter can be large. It is not unusual forthe fully expanded diameter to be 3 to 4 times larger than the crimpeddiameter. A self-expanding stent is designed, through choice ofmaterial, geometry, and manufacturing techniques, to expand from thecrimped diameter to an expanded diameter once it is released into theintended vessel.

The stent of the present invention comprises a helical strut bandhelically wound about an axis of the strut. The helical strut bandcomprises a wave pattern of strut elements having a plurality of peakson either side of the wave pattern. A plurality of coil elements arehelically wound about an axis of the stent and progress in the samedirection as the helical strut band. The coil elements are typicallyelongated where the length is much longer than the width. The coilelements interconnect at least some of the strut elements of a firstwinding to at least some of the strut elements of a second winding ofthe helical strut band at or near the peaks of the wave pattern. In thestent of the present invention, a geometric relationship triangle isconstructed having a first side with a leg length L_(C) being theeffective length of the coil element between the interconnected peaks ofa first and second winding of the helical strut band, a second side witha leg length being the circumferential distance between the peak of thefirst winding and the peak of the second winding interconnected by thecoil element divided by the sine of an angle A_(s) of the helical strutband from a longitudinal axis of the stent, a third side with a leglength being the longitudinal distance the helical strut band progressesin 1 circumference winding (P1) minus the effective strut length L_(s),a first angle of the first leg being 180 degrees minus the angle A_(s),a second angle of the second leg being an angle A_(c) the coil elementgenerally progresses around the axis of the stent measured from thelongitudinal axis and a third angle of the third leg being the angleA_(s) minus the angle A_(c), wherein a ratio of the first leg lengthL_(C) to a length L_(S) multiplied by the number of adjacent wavepattern of the strut elements forming the helical strut band, N_(S) isgreater than or equal to about 1. This value is defined as thecoil-strut ratio and numerically is represented by coil-strutratio=Lc/Ls*Ns.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing description, as well as further objects, features, andadvantages of the present invention will be understood more completelyfrom the following detailed description of presently preferred, butnonetheless illustrative embodiments in accordance with the presentinvention, with reference being had to the accompanying drawings, inwhich:

FIG. 1 is a schematic drawing of the stent delivery system in accordancewith the present invention.

FIG. 2 is a detailed enlarged view of X-X section shown in FIG. 1 justprior to stent deployment.

FIG. 3 is a detailed enlarged view of X-X section shown in FIG. 1 justprior to the recapturing.

FIG. 4 is a detailed enlarged view of X-X section shown in FIG. 1 withan alternate embodiment configuration.

FIG. 5 is a detailed enlarged view of X-X section shown in FIG. 1 withan alternate embodiment configuration

FIG. 6 is a view of Z-Z section shown in FIG. 5 with an alternateembodiment configuration.

FIG. 7 is a detailed enlarged view of X-X section shown in FIG. 1 justprior to the start of stent deployment.

FIG. 8 is a detailed enlarged view of X-X section shown in FIG. 1 duringstent deployment.

FIG. 9 is a schematic drawing of the stent delivery system in accordancewith the present invention.

FIG. 10 is a plan view of a first embodiment of a stent in accordancewith the present invention, the stent being shown in a partiallyexpanded state.

FIG. 11 is a detailed enlarged view of portion A shown in FIG. 1.

FIG. 12 is a plan view of an alternate embodiment of the stent.

FIG. 13 is an enlarged detailed view of portion B shown in FIG. 3.

FIG. 14 is a plan view of an alternate embodiment of the stent.

FIG. 15 is a plan view of an alternate embodiment of the stent.

FIG. 16 is a plan view of an alternate embodiment of the stent.

FIG. 17 is a detailed enlarged view of portion C shown in FIG. 7.

FIG. 18 is a plan view of an alternate embodiment of the stent.

FIG. 19 is a schematic diagram of an alternate embodiment for a coilelement of the stent.

FIG. 20 is a detailed enlarged view of portion D shown in FIG. 14.

FIG. 21 is a detailed enlarged view of X-X section shown in FIG. 1 withan alternate embodiment configuration

DETAILED DESCRIPTION OF THE INVENTION

The self expanding stent delivery system 10 of the present invention isshown in FIG. 1 and is comprised of inner and outer coaxial members, forexample a shaft or tube. The outer tube which is also known as outersheath 11, constrains stent 12 in a crimped or radially compressedstate. The inner members can be comprised of multiple componentsincluding distal tip 8, guide wire tube 14 and pusher 16 to react theaxial forces placed on the stent as the outer sheath is retracted todeploy the stent. Pusher 16 can also act as a proximal stop. Otherelements of the stent delivery system can include luer lock hub 6attached to the proximal end of pusher 16, handle 3 attached to outersheath 11 that incorporates luer port 4 such that the space between theinner members and outer sheath 11 can be flushed with saline solutionsto remove any entrapped air. Pusher 16 is sometimes a compositestructure of multiple components, such as a stainless steel tube at theproximal end and a polymer tube inside outer sheath 11.

Stent delivery system 10 of the present invention, shown in the detailview of X-X section, FIG. 2, is comprised of outer sheath 11, a deliverycatheter in which stent 12 is constrained in a crimped, or radiallycompressed state. Stent delivery system 10 can be referred to ascatheter delivery system as a delivery catheter. Slider 13 is positionedto interface with the inside diameter of crimped stent 12. Slider 13 iscoaxial with guide wire tube 14 and slider 13 is free to rotate andslide relative to guide wire tube 14. Distal stop 15 is fixed to guidewire tube 14 at a position distal to slider 13. Pusher 16 is positionedproximal to stent 12 and slider 13 and reacts the axial forcestransmitted to stent 12 as outer sheath 11 is retracted to deploy thestent and provides a proximal stop. Stent 12 and slider 13 are free tomove, translate or rotate, within outer sheath 11 and relative to guidewire tube 14 as outer sheath 11 is retracted and stent 12 is deployed.This is advantageous when the stent design is such that stent 12shortens in length and/or rotates as it expands from the crimped stateto a larger diameter expanded state. The delivery system of the presentinvention allows the stent movement to occur inside outer sheath 11instead of inside the body lumen. Before outer sheath 11 is fullyretracted, thereby releasing stent 12, the stent can be recaptured bymoving guide wire tube 14 and attached distal stop 15 proximallyrelative to stent 12 and slider 13 until distal stop 15 contacts slider13, as shown in detail view of X-X section, FIG. 3. Because stent 12 andslider 13 are intimate contact with each other, outer sheath 11 can bemoved distally relative to stent 12, slider 13, guide wire tube 14 anddistal stop 15, there by recapturing stent 12 inside outer sheath 11. Inthis embodiment, pusher 16 is in contact with stent 12 as outer sheath11 is retracted to deploy stent 12.

In an alternate embodiment, slider 13 is designed to interface with theinside diameter of stent 12 and contact pusher 16 as outer sheath 11 isretracted, as shown in FIG. 4. This embodiment reduces the axially loaddirectly placed on stent 12 during stent deployment.

In the embodiment described above, slider 13 is coaxial with guide wiretube 14 and slider 13 is free to rotate and slide relative to guide wiretube 14. Guide wire tube 14 can be hollow, forming a lumen that runs thelength of the stent delivery system to accommodate a guide wire which isoften used to facilitate locating the stent delivery system in thetarget vessel, artery, duct or body lumen. Alternatively, guide wiretube 14 can be a non-hollow solid shaft 18, as shown in FIG. 5.

In an alternate embodiment axial force at the proximal end of the stentis reacted by a proximal stop 19, attached to non-hollow shaft 18, suchthat proximal stop 19 and non-hollow shaft are a unitary member as shownin FIG. 21. Proximal stop 19 and non-hollow shaft 18 could be made fromdifferent materials that are affixed together or made from the samematerial.

In an alternate embodiment shown in Z-Z section view, FIG. 6, slider 13is formed of a structure where a portion of slider 13 is a polymer thatis molded or formed to inside diameter 21 of stent 12 and/or sidewall 22of stent 12. Slider 13 can be a composite or laminated structurecomprising polymer portion 23 interfacing with stent 12 and rigidportion 24 near the inside diameter of slider 13.

In another embodiment as shown in detail view of X-X section, FIG. 7 andFIG. 8, spring element 25 is incorporated into pusher 16 such thatspring element 25 is compressed as the axial force at the proximal endof stent 12 increases until outer sheath 11 starts to move in a proximaldirection relative to stent 12. As stent 12 deploys, spring element 25continues to react the axial load at the proximal end of stent 12 andsimultaneously pushes the proximal end of stent 12 distally as stent 12foreshortens coming out of outer sheath 11. FIG. 7 shows spring element25 in an uncompressed state prior to the start of stent 12 deploymentwhere stent 12 is not under an axial load. FIG. 8 shows spring element25 in a compressed state after the start of deployment where stent 12 isunder an axial load, where X2<X1. As stent 12 expands out of outersheath 11 the axial load on stent 12 will typically decrease from a peakload near the beginning of the deployment. As the axial load decreases,the spring force will push the proximal end of stent 12 forward to biasany movement of stent 12 due to foreshortening occurring at the proximalend of stent 12, such that the proximal end of stent 12 moves distallyinstead of the distal end of stent 12 moving proximally.

In an alternate embodiment, spring element 26 can be incorporated at theproximal end of stent delivery system 10, where distal end 27 of springelement 26 effectively interfaces with pusher 16, and proximal end 28 ofspring element 26 is fixed, such that pusher 16 compresses springelement 26 as the axial force at the proximal end of stent 12 increasesuntil outer sheath 11 starts to move in a proximal direction relative tostent 12. As stent 12 deploys, spring element 26 moves pusher 16proximally as stent 12 foreshortens coming out of outer sheath 11.

FIG. 10 with detail shown in FIG. 11 illustrates stent 500 which can beused in stent delivery system 10. FIG. 10 is a plan view of a firstembodiment of stent 500 in accordance with the teachings presentinvention shown in a partially expanded state. As used herein, the term“plan view” will be understood to describe an unwrapped plan view. Thiscould be thought of as slicing open a tubular stent along a lineparallel to its axis and laying it out flat. It should therefore beappreciated that, in the actual stent, the top edge of FIG. 10 will bejoined to the lower edge. Stent 500 is comprised of helical strut band502 interconnected by coil elements 507. Side-by-side coil elements 507form coil band 510. Coil band 510 is formed as a double helix withhelical strut band 502 and progresses from one end of the stent to theother. Helical strut band 502 comprises a wave pattern of strut elements503 that have peaks 508 on either side of the wave pattern and legs 509between peaks 508. Coil elements 507 interconnect strut elements 503 ofhelical strut band 502 through or near peaks 508. NSC portion 505 ofhelical strut band 502 is defined by the number of strut elements 503(NSC) of helical strut band 502 between coil element 507 as helicalstrut band 502 progresses around stent 500. The number of strut elements503 (NSC) in NSC portion 505 of helical strut band 502 is more than thenumber of strut elements 503 (N) in one circumference winding of helicalstrut band 502. The number of strut elements 503 (NSC) in NSC portion505 is constant.

In this embodiment, stent 500 has N=12.728 helical strut elements 503 inone circumference winding of helical strut band 502 and has NSC=16.5helical strut elements 503 in NSC portion 505. CCDn portion 512 of NSCportion 505 of helical strut band 502 is defined by the number of strutelements 503 (CCDn) equal to NSC minus N. The number of strut elements503 (CCDn) in CCDn portion 512 and the number of strut elements 503 (N)in one circumference winding of helical strut band 502 does not need tobe constant at different diameter size states of stent 500. Stent 500has CCDn=3.772 helical strut elements 503 in CCDn portion 512. Becausethis connectivity needs to be maintained at any diameter size state ageometric relationship between the helical strut band 502 and coilelement 507 can be described by geometric relationship triangle 511.Geometric relationship triangle 511 has a first side 516 with a leglength equal to the effective length (Lc) 530 of coil element 507, asecond side 513 with a leg length equal to circumferential coil distance(CCD) 531 of CCDn portion 512 of helical strut band 502 divided by thesine of an angle A_(s) 535 of helical strut band 502 from thelongitudinal axis of stent 500, a third side 514 with a leg length (SS)532 equal to the longitudinal distance (P1) 534 helical strut band 502progresses in 1 circumference winding minus the effective strut lengthL_(s) 533, a first angle 537 of first side 516 is equal to 180 degreesminus angle A_(s) 535, a second angle 536 of second side 513 is equal tothe angle A_(c) 536 of coil element 507 from the longitudinal axis ofstent 500 and a third angle 538 of third side 514 equal to angle A_(s)535 minus angle A_(c) 536. If the circumferential strut distance (P_(s))539 of helical strut element 503 is the same for all helical strutelements 503 in CCDn portion 512, circumferential coil distance CCD 531is equal to the number of helical strut elements 503 in the CCDn portion512 multiplied by the circumferential strut distance (P_(s)) 539. Thedistances in any figure that shows a flat pattern view of a stentrepresent distances on the surface of the stent, for example verticaldistances are circumferential distances and angled distances are helicaldistances. First side 516 of geometric relationship triangle 511 isdrawn parallel to the linear portion of coil element 507 such that thecoil angle Ac 536 is equal to the angle of the linear portion of coilelement 507. If coil element 507 does not have a substantially linearportion, but progresses about the stent in a helical manner, anequivalent coil angle 536 could be used to construct the geometricrelationship triangle 511. For instance if coil element 507 is a wavycoil element 907, as shown in FIG. 19, line 901 could be drawn fittedthrough the curves of the wavy coil element 907 and line 901 can be usedto define coil angle 536.

Stent 400 shown in FIGS. 12 and 13 is similar to stent 500 in that it iscomprised of helical strut band 402 interconnected by coil elements 507.Stent 400 is different in that helical strut band 402 is comprised oftwo adjacent wave patterns of strut elements 403 a and 403 b that havepeaks 508 on either side of the wave pattern. Strut element 403 a beingconnected to strut element 403 b. Similar to helical strut band 502,helical strut band 402 also has a NSC portion 405 and a CCDn portion412. Helical strut band 402 can be defined as having a number Ns of wavepatterns of strut elements equal to 2. Helical strut band 502 can bedefined as having a number Ns of wave patterns of strut elements equalto 1. In an alternate embodiment, the stent of the present invention canhave a helical strut band with a number Ns of wave patterns of strutelements equal to 3, which would be a triple strut band. In an alternateembodiment, the stent of the present invention could have a helicalstrut band with a number Ns of wave patterns of strut elements equal toany integer. Stents with helical strut bands having a number Ns of wavepatterns of strut elements equal to or greater than 2 provide anadvantage in that the helical strut band would form a closed cellstructure with smaller cell size which is desired when there isadditional risk of embolism. Stents with smaller cell sizes tend to trapplaque or other potential embolic debris better than stents with largercell sizes.

Stent structures described provides the combination of attributesdesirable in a stent when the coil-strut ratio, ratio of Lc to Lsmultiplied by the number of wave patterns of strut elements Ns in thehelical strut band (Lc multiplied by Ns divided by Ls), is greater thanor equal to 1. For example the coil-strut ratio for stent 500 is 2.06and for stent 400 is 2.02. Stent 200 shown in FIG. 18 has a similarstructure to stent 500. The coil-strut ratio for stent 200 is about1.11.

In order for the stent of the present invention to crimped to a smallerdiameter, the geometry of the structure undergoes several changes.Because of the helical nature of the helical strut band, strut angleA_(s) must get smaller as the stent diameter decreases. Because of theinterconnectivity between a first winding of the helical strut band anda second winding of the helical strut band created by the coil element,the angle of the element A_(c) must also get smaller, or becomeshallower, to accommodate the smaller strut angle A_(s). If the angle ofcoil element A_(c) can not become shallower or is difficult to becomeshallower as the stent crimps and stent angle A_(s) gets smaller, thecoil elements will tend to interfere with each other and prohibitcrimping or require more force to crimp. The changing of the angle ofthe coil element during crimping is facilitated if the coil-strut ratiois greater than 1. Coil-strut ratios less than 1 tend to stiffen thecoil element such that more force is required to bend the coil elementto a shallower angle during the crimping process, which is notdesirable.

Helical strut band 602 of stent 600, shown in FIG. 14, transitions toand continues as an end strut portion 622 where the angle of the windingAT1 of the wave pattern of strut elements 624 a forming end strutportion 622 is larger than the angle of the helical strut band A. Endstrut portion 622 includes a second winding of the wave pattern of strutelements 624 b where the angle AT2 of the second winding is larger thanthe angle of the first winding AT1. Strut elements 603 of helical strutband 602 are interconnected to strut elements 624 a of the first windingof end strut portion 622 by a series of transitional coil elements 623that define transition coil portion 621. All strut elements 624 a of thefirst winding of end portion 622 are connected by coil elements 623 tothe helical strut band 602. Peaks 620 of helical strut band 602 are notconnected to end strut portion 622. Transitional coil portion 621 allowsend strut portion 622 to have a substantially flat end 625. Helicalstrut band 402 of stent 400 transitions to and continues as an endportion where the angle of the first winding AT1 of the wave pattern ofstrut elements forming of the end portion is larger than the angle ofthe helical strut band As. The angle of the second winding AT2 is largerthan AT1, and the angle of subsequent windings of the end portion arealso increasing (i.e. AT1<AT2<AT3<AT4). As shown in FIG. 20, stent 600includes one peak 626 of end strut portion 622 connected to two peaks620 of helical strut band 602 by transitional coil elements 623.

The accompanying definitions are described below.

-   -   (N)—Number of helical strut elements in one circumference        winding of the helical strut member.    -   (A_(s))—Angle of helical strut band winding measured from the        longitudinal axis of the stent.    -   (A_(c))—Effective angle of coil element measured from the        longitudinal axis of the stent.    -   (P1)—Longitudinal distance (pitch) the strut member progresses        in 1 circumference winding. Equal to the circumference of the        stent divided by the arctangent of A_(s).    -   (P_(s))—Circumferential distance (pitch) between strut legs of a        helical strut element of the helical strut band. Assuming the        circumferential strut pitch is equal for all strut elements of        the helical strut band, the circumferential strut pitch is equal        to the circumference of the stent divided by N.    -   (NSC)—Number of strut elements of the strut band between a        helical element as the strut member progresses    -   (CCDn)—Number of strut elements of the strut band between        interconnected strut elements, equal to NSC minus N    -   (CCD)—Circumferential Coil Distance is the circumferential        distance between interconnected strut elements, equal to the        CCDn times the P_(s) if the Ps is equal for all strut elements        in the CCDn portion.    -   (Lc)—Effective length of the helical element as defined by the        geometric relationship triangle described in table 1.    -   (SS)—Strut Separation as defined in the geometric relationship        triangle described in table 1.    -   (Ls)—Effective Strut Length. Equal to P1 minus SS.    -   (Ns)—Number of adjacent wave patterns of the strut elements        forming the helical strut band.    -   Coil-Strut ratio—Ratio of L_(c) to a length L_(s) multiplied by        the number of adjacent wave pattern of the strut elements        forming the helical strut band, N_(s). Numerically equal to        Lc/Ls*Ns.    -   Strut length-Strut Separation ratio—Ratio of the effective strut        length (Ls) to the Strut Separation (SS), numerically equal to        Ls/SS.

TABLE 1 Leg Length Angle Side 1 Lc 180° minus A_(s) Side 2 CCD dividedby sin(A_(s)) A_(c) Side 3 SS A_(s) minus A_(c)

In one embodiment, the difference between the strut angle, A_(s), andcoil angle, A_(c), is more than about 20 degrees. Because of thenecessity of the coil angle to become shallower as the stent is crimped,if the coil angle and the strut angle in the expanded state are tooclose to each other there is increased difficulty in crimping the stent.

For the stent of the present invention the Strut length-Strut Separationratio is a measure of the relative angle of the strut angle and coilangle. Stents with Strut length-Strut Separation ratios less than about2.5 have improved crimping behavior. Stent attributes can further beimproved if the angle of the strut member is between 55 degrees and 80degrees and the coil angle is between 45 degrees and 60 degrees in theexpanded state. Additionally, steeper coil angles A_(c) in the expandedstate make crimping the stent of the present invention more difficult.Coil angles of less than 60 degrees in the expanded state facilitatecrimping the stent of the present invention.

For the stent of the present invention, in addition to the coil anglechanging during crimping, the helical strut band rotates about thelongitudinal axis of the stent to accommodate the connectivity betweensubsequent windings of helical strut bands during crimping resulting inmore windings of the helical strut band along the length of the stentwhen the stent is crimped. In one embodiment, the longitudinal pitch ofthe helical strut band (P1) is approximately the same in both theexpanded state and crimped state. Considering that an increase ofhelical strut band windings along the length of the stent when the stentis crimped contributes to stent foreshortening it is advantageous forthe stent of the present invention to have an approximated increase inthe amount of helical strut band windings of less than about 30% whencrimped, preferably less than about 26%. A 26% increase in helical strutband winding corresponds to about 20% foreshortening which is consideredthe maximum clinically useful amount of foreshortening (Serruys,Patrick, W., and Kutryk, Michael, J. B., Eds., Handbook of CoronaryStents, Second Edition, Martin Dunitz Ltd., London, 1998.) herebyincorporated by reference in its entirety into this application.

FIG. 15 is a plan view of another embodiment of stent 700 in accordancewith the teachings of the present invention. Helical strut band 702progresses helically from one end of stent 700 to the other. Each strutelement 703 is connected to a strut in a subsequent winding of helicalstrut band 702 by coil element 707. Strut element 703 includes legportions 709. Each of leg portions 709 has an equal length.

FIG. 16, with detail shown in FIG. 17, is a plan view of anotherembodiment of stent 800. In this embodiment, coil element 807 includescurved transition portion 852 at ends 853 and 854. Curved transitionportion 852 connects to strut element 803.

Stent 800 includes transitional helical portions 859 and end strutportions 858 at either end 861 of stent 800. End strut portions 858 areformed of a pair of connected strut windings 860. Coil element 807 iscomprised of two coil portions 807 a and 807 b which are separated bygap 808, as shown in FIG. 17. Gap 808 can have a size equal to zerowhere coil portions 807 a and 807 b are touching. Gap 808 terminatesnear ends 853 and 854. Gap 808 can terminate anywhere along the lengthof coil 807 or at multiple points along coil 807 such that the gap wouldhave interruptions along coil 807.

Stents 400, 500, 600, 700 and 800 are made from a common material forself expanding stents, such as Nitinol nickel-titanium alloy (Ni/Ti), asis well known in the art.

In an alternate embodiment, stent 12 can be a stent as described in U.S.Pat. No. 7,556,644 hereby incorporated by reference into thisapplication.

The stents of the present invention may be placed within vessels usingprocedures well known in the art. The stents may be loaded into theproximal end of a catheter and advanced through the catheter andreleased at the desired site. Alternatively, the stents may be carriedabout the distal end of the catheter in a compressed state and releasedat the desired site. The stents may either be self-expanding or expandedby means such as an inflatable balloon segment of the catheter. Afterthe stent(s) have been deposited at the desired intralumenal site, thecatheter is withdrawn.

The stents of the present invention may be placed within body lumen suchas vascular vessels or ducts of any mammal species including humans,without damaging the lumenal wall. For example, the stent can be placedwithin a lesion or an aneurysm for treating the aneurysm. In oneembodiment, the flexible stent is placed in a super femoral artery uponinsertion into the vessel. In a method of treating a diseased vessel orduct a catheter is guided to a target site of a diseased vessel or duct.The stent is advanced through the catheter to the target site. Forexample, the vessel can be a vascular vessel, femoropopliteal artery,tibial artery, carotid artery, iliac artery, renal artery, coronaryartery, neurovascular artery or vein.

Stents of the present invention may be well suited to treating vesselsin the human body that are exposed to significant biomechanical forces.Stents that are implanted in vessels in the human body that are exposedto significant biomechanical forces must pass rigorous fatigue tests tobe legally marketed for sale. These tests typically simulate loading ina human body for a number of cycles equivalent to 10 years of use.Depending on the simulated loading condition, the number of test cyclesmay range from 1 to 400 million cycles. For example, stents that areintended to be used in the femorpopliteal arteries may be required topass a bending test where the stent is bent to a radius of about 20 mm 1to 10 million times or axially compressed about 10% 1 to 10 milliontimes.

It is to be understood that the above-described embodiments areillustrative of only a few of the many possible specific embodiments,which can represent applications of the principles of the invention.Numerous and varied other arrangements can be readily devised inaccordance with these principles by those skilled in the art withoutdeparting from the spirit and scope of the invention. For example, astent could be made with only right-handed or only left-handed helicalportions, or the helical strut band could have multiple reversals inwinding direction rather than just one. Also, the helical strut bandcould have any number of turns per unit length or a variable pitch, andthe strut bands and/or coil bands could be of unequal length along thestent.

The stent delivery system of the present invention can be used with anystent that allows recapturing after partial deployment.

1. A delivery system for a self-expanding stent, said system comprises:an inner member located coaxially with an outer member, said innermember and said outer member including a distal and proximal end; apusher positioned at a proximal end of said inner member; and a sliderlocated coaxially with said inner member and positioned within andcontacting an inner diameter of said stent, wherein before deployment ofthe stent, the stent is constrained within an inner diameter of saidouter member and during deployment of the stent said slider can rotateabout and move longitudinally along said inner member allowing saidstent to move distally or rotate within said outer member as said outermember is retracted to deploy said stent.
 2. The system of claim 1wherein said pusher and said inner member move distally as said outermember retracts proximally during deployment of said stent toaccommodate foreshortening of said stent.
 3. The system of claim 1further comprising: a distal stop attached to said inner member at aposition distal to said slider.
 4. The system of claim 3 wherein beforesaid outer member is fully retracted to release said stent, said innermember and said distal stop attached to said inner member move proximalto said stent and said slider until said distal stop contacts saidslider, thereby re-constraining said stent within said outer member. 5.The system of claim 1 wherein said slider contacts said pusher as saidouter member is retracted.
 6. The system of claim 1 wherein said pusherprovides a proximal stop.
 7. The system of claim 1 wherein said outermember is an outer sheath.
 8. The system of claim 1 wherein said innermember is a guide wire tube.
 9. The system of claim 8 wherein said guidewire tube is hollow.
 10. The system of claim 1 wherein said inner memberis a solid shaft.
 11. The system of claim 1 wherein said slider isformed to said inside diameter of said stent on an inner wall of saidstent.
 12. The system of claim 1 wherein said slider comprises an outerportion formed of a polymer and said outer portion of said slider ismolded to said inner diameter of said stent.
 13. The system of claim 1wherein said slider is a laminated structure formed of an outer portionand an inner portion, said outer portion of said slider is formed of apolymer, said outer portion of said slider is molded to said innerdiameter of said stent and said inner portion of said slider is formedof a rigid portion.
 14. The system of claim 1 further comprising: a biaselement coupled to a distal end of said pusher, wherein said biaselement biases axial movement of said stent inside the delivery systemand pushes a proximal end of said stent distally during said deploymentof said stent.
 15. The system of claim 1 wherein said self expandingstent comprises: a helical strut band helically wound about an axis ofsaid stent, said helical strut band comprising a wave pattern of strutelements, said wave pattern having a plurality of peaks on either sideof said wave pattern; and a plurality of coil elements helically woundabout an axis of said stent, said coil elements progressing in the samedirection as said helical strut band interconnecting at least some ofsaid peaks of a first winding through or near to at least some of saidpeaks of a second winding of said helical strut band, wherein ageometric relationship triangle is constructed having a first side witha leg length L_(C) being the effective length of said coil elementbetween the interconnected peaks of said first and second winding ofsaid helical strut band, a second side with a leg length being thecircumferential distance between said peak of said first winding andsaid peak of said second winding interconnected by said coil elementdivided by the sine of an angle A_(s) of said helical strut member froma longitudinal axis of said stent, a third side with a leg length beingthe longitudinal distance said helical strut band progresses in 1circumference winding (P1) minus the effective strut length L_(s), afirst angle of said first leg being 180 degrees minus said angle A_(s),a second angle of said second leg being an angle A_(c) of said coilelement from said longitudinal axis and a third angle of said third legbeing said angle A_(s) minus said angle A_(c), wherein a coil-strutratio, is a ratio of said first leg length L_(C) to a length L_(S)multiplied by the number of adjacent said wave pattern of said strutelements forming said helical strut band, N_(S) is greater than or equalto about
 1. 16. The system of claim 15 wherein said coil-strut ratio ofis greater than 2.0.
 17. The system of claim 15 wherein said helicalstrut band comprises: a plurality of said wave pattern of strut elementswherein strut elements of each of said wave patterns are connected toone another.
 18. The system of claim 17 comprising two said wavepatterns.
 19. The system of claim 17 comprising three said wavepatterns.
 20. The system of claim 15 further comprising: a strut portionconnected to an end of said helical strut band, said strut portion woundabout said axis of said stent and comprising a plurality of strutelements, said strut portion is wound about said axis of said stent withan acute angle formed between a plane perpendicular to said axis of saidstent and said strut portion winding that is smaller than an acute angleformed between the plane perpendicular to said axis of said stent andthe winding of said helical strut band; and transitional helicalportions interconnected between said strut portion and a winding of saidhelical strut band adjacent said strut portion, said transitionalhelical band comprising transitional helical elements, said transitionalhelical elements connecting at least some of said coil elements of saidwinding of said helical strut band adjacent said strut portion and atleast some of said strut elements of said strut portion.
 21. The systemof claim 20 wherein adjacent ones of said transitional helical elementsextending progressively at a shorter length around the circumference ofsaid stent as the winding of said strut portion progresses away fromsaid helical strut band.
 22. The system of claim 20 wherein some of saidcoil elements of said helical strut band are not connected to said strutportion.
 23. The system of claim 15 wherein each of said leg portions insaid pair of leg portions have an equal length.
 24. The system of claim15 wherein said coil elements include a curved transition at either endthereof, said curved transition portion connecting to said peaks of saidhelical strut member.
 25. The system of claim 15 wherein said coilelements comprise a pair of coil portions separated by a gap.
 26. Thesystem of claim 1 wherein the self expanding stent comprises: a helicalstrut band helically wound about an axis of said stent, said helicalstrut band comprising a wave pattern of strut elements, said wavepattern having a plurality of peaks on either side of said wave pattern;and a plurality of coil elements helically wound about an axis of saidstent, said coil elements progressing in the same direction as saidhelical strut band interconnecting at least some of said peaks of afirst winding through or near to at least some of said peaks of a secondwinding of said helical strut band, wherein a geometric relationshiptriangle is constructed having a first side with a leg length L_(C)being the effective length of said coil element between theinterconnected peaks of said first and second winding of said helicalstrut band, a second side with a leg length being the circumferentialdistance between said peak of said first winding and said peak of saidsecond winding interconnected by said coil element divided by the sineof an angle A_(s) of said helical strut member from a longitudinal axisof said stent, a third side with a leg length being the longitudinaldistance said helical strut band progresses in 1 circumference winding(P1) minus the effective strut length L_(S), a first angle of said firstleg being 180 degrees minus said angle A_(s), a second angle of saidsecond leg being an angle A_(c) of said coil element from saidlongitudinal axis and a third angle of said third leg being said angleA_(s) minus said angle A_(c).